As far as I know, there aren’t many poems containing the word “loitering”. Loitering is something shady characters do in public lavatories or when casing a joint. Loitering, at least according to the police, is done “with intent”. In contrast, the loitering of Keats’ knight has no purpose:

Oh what can ail thee, knight-at-arms,
Alone and palely loitering?
The sedge has withered from the lake,
And no birds sing.

Oh what can ail thee, knight-at-arms,
So haggard and so woe-begone?
The squirrel's granary is full,
And the harvest's done.

I see a lily on thy brow,
With anguish moist and fever-dew,
And on thy cheeks a fading rose
Fast withereth too.

I met a lady in the meads,
Full beautiful - a faery's child,
Her hair was long, her foot was light,
And her eyes were wild.

I made a garland for her head,
And bracelets too, and fragrant zone;
She looked at me as she did love,
And made sweet moan.

I set her on my pacing steed,
And nothing else saw all day long,
For sidelong would she bend, and sing
A faery's song.

She found me roots of relish sweet,
And honey wild, and manna-dew,
And sure in language strange she said -
'I love thee true'.

She took me to her elfin grot,
And there she wept and sighed full sore,
And there I shut her wild wild eyes
With kisses four.

And there she lulled me asleep
And there I dreamed - Ah! woe betide! -
The latest dream I ever dreamt
On the cold hill side.